Journal Article

A comprehensive population synthesis study of post-common envelope binaries

P. J. Davis, U. Kolb and B. Willems

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 1, pages 179-195
Published in print March 2010 | ISSN: 0035-8711
Published online March 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16138.x
A comprehensive population synthesis study of post-common envelope binaries

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We apply population synthesis techniques to calculate the present-day population of post-common envelope binaries (PCEBs) for a range of theoretical models describing the common envelope (CE) phase. Adopting the canonical energy budget approach, we consider models where the ejection efficiency αCE is either a constant or a function of the secondary mass. We obtain the envelope binding energy from detailed stellar models of the progenitor primary, with and without the thermal and ionization energy, but we also test a commonly used analytical scaling. We also employ the alternative angular momentum budget approach, known as the γ-algorithm. We find that a constant, global value of αCE≳ 0.1 can adequately account for the observed population of PCEBs with late spectral-type secondaries. However, this prescription fails to reproduce IK Pegasi (IK Peg), which has a secondary with spectral type A8. We can account for IK Peg if we include thermal and ionization energy of the giant's envelope, or if we use the γ-algorithm. However, the γ-algorithm predicts local space densities that are 1 to 2 orders of magnitude greater than estimates from observations. In contrast, the canonical energy budget prescription with an initial mass ratio distribution that favours unequal initial mass ratios (n(qi) ∝q−0.99i) gives a local space density which is in good agreement with observations, and best reproduces the observed distribution of PCEBs. Finally, all models fail to reproduce the sharp decline for orbital periods, Porb≳ 1 d in the orbital period distribution of observed PCEBs, even if we take into account selection effects against systems with long orbital periods and early spectral-type secondaries.

Keywords: methods: numerical; methods: statistical; binaries: close; stars: evolution

Journal Article.  12371 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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